With the blooming demand for container transportation all over the world and the growth in throughput of container terminals, requirements on container loading/unloading device and process is also improved. There is a need for a new container loading/unloading device and system that has higher efficiency, so as to meet the requirements on loading/unloading production efficiency of a terminal for a scaled, speed and automatic transportation of containers.
From 1990s, with the development of the world economic and trade, the amount of transportation of containers increases, new techniques, especially automatic control techniques of quayside container cranes develop quickly. However, loading/unloading systems that are currently used for a container terminal still have the following problems.
Generally, a container terminal may be divided into a front area (a quayside area) and a rear area (a yard area) and a middle area. Quayside cranes located in the front area load/unload containers with a container ship, a yard at the rear area is used to stack containers. Trucks are used to transport containers between the front area and the rear area.
For transportation between the quayside cranes and the yard, nowadays, plane trucks driven by diesel engine are used to achieve transportation between a front area and a rear area. For an unloading process, the quayside cranes unload containers from a ship to the plane trucks, the plane trucks transport the containers to a yard, then yard cranes hoist the containers from the plane trucks and put them on the yard. For a loading process, the yard cranes hoist containers from the yard and put them on plane trucks, the plane trucks transport the containers to a position below the quayside cranes, the quayside cranes load the containers to the ship. Attempts are made for an automatic loading/unloading process for containers, for example, Port of Rotterdam in Netherlands and Hamburger Harbor in Deutschland introduce Automatic Guided Vehicles (AVG) to replace the plane trucks driven by drivers. AGVs are still driven by diesel engine, there is no improvement in energy source. Additionally, AGVs are very expensive, and must move along a single guide line which is buried in advance in a same plane. If one of the AGVs is failed, the whole system is stopped. Unfortunately, failure possibility of AGVs is very high because of the complex structure, failures of AGVs are also difficult to deal with. Therefore, the current attempts of automatic systems face a low efficiency and a high cost.
Whatever the traditional manual manner, or the automatic attempts, the loading/unloading mode of containers can be concluded as: a plane transportation mode consists of quayside cranes located at a quayside area of a container terminal, yard cranes located at a yard area of the container terminal, and diesel engine driven vehicles, such as container trucks, cross transportation trucks, AGVs moving between the quayside cranes and the yard cranes for transporting the containers. The loading/unloading mode needs dozens or even hundreds of diesel engine driven vehicles, for ensuring a smooth movement of these vehicles, a large space must be reserved between the quayside and the yard, which occupies a considerable size of ground. Even a large space is provided, the traffic within the container terminal is still very crowd because all of the vehicles move in a same plane. The vehicles work in a low efficiency, not being able to timely transport containers, and decrease the loading/unloading efficiency of the whole container terminal. Efficiency of vehicles becomes a bottle-neck of loading/unloading efficiency of the container terminal. Furthermore, oil is expensive, operation cost of the container terminal is high and benefit of the container terminal is getting lower. Another problem is, burning oil produces a large amount of exhaust gas and noise, seriously pollute the environment. Maintenance fee of the diesel engine driven vehicles is also very high. The plane transportation technique falls behind, and can not facilitate infomationization, automation and intelligentization of the container terminal.